M2 Macrophagy-derived exosomal miRNA-5106 induces bone mesenchymal stem cells towards osteoblastic fate by targeting salt-inducible kinase 2 and 3

Osteogenic effect and mechanism of IL-10 in diabetic rat jaw defect mode

OBJECTIVE

The aim of this study was to investigate the effect of IL-10 on the phenotype polarization of macrophages and osteogenesis in diabetes mellitus type 2 (T2DM) rat jaw defects.

METHODS

Lipopolysaccharide (LPS) and interleukin-10 (IL-10) were chosen to induce the polarization of macrophages. In vitro assessment included wound-healing assay, western blotting, and alizarin red staining after co-culture of the bone marrow-derived mesenchymal stem cells (BMSCs) and induced macrophages. For in vivo study, IL-10 was loaded on GelMA-Heparin and applied to bone defects of the alveolar ridge in diabetic rats, while Bio-Oss Collagen, simple GelMA-Heparin, and blank control groups were set for contrast experiment. The mandibles of rats were processed for micro-computed tomography, histology, and immunohistochemistry 1 week and 4 weeks after the operation.

RESULTS

IL-10 induced expression of arginase 1, TGF-β1, EGR2, and Mannose Receptor (CD206), whereas LPS induced expression of iNOS, TNF-α, IL-6, CD80. The BMSCs co-cultured with macrophages induced by IL-10 showed increased migration, osteogenic differentiation, and mineralization in vitro. Notably, the IL-10-laden GelMA-Heparin group showed quicker new bone formation and a higher M2/M1 ratio of macrophages in the jawbone defect area compared with the control groups.

CONCLUSIONS

IL-10 can stably induce macrophages to M2 type, thereby influencing BMSCs and improving the osteogenesis of jaw bone defects.

Mesenchymal Stem Cell-Derived Extracellular Vesicles in Bone-Related Diseases: Intercellular Communication Messengers and Therapeutic Engineering Protagonists

Extracellular vesicles (EVs) can deliver various bioactive molecules among cells, making them promising diagnostic and therapeutic alternatives in diseases. Mesenchymal stem cell-derived EVs (MSC-EVs) have shown therapeutic potential similar to MSCs but with drawbacks such as lower yield, reduced biological activities, off-target effects, and shorter half-lives. Improving strategies utilizing biotechniques to pretreat MSCs and enhance the properties of released EVs, as well as modifying MSC-EVs to enhance targeting abilities and achieve controlled release, shows potential for overcoming application limitations and enhancing therapeutic effects in treating bone-related diseases. This review focuses on recent advances in functionalizing MSC-EVs to treat bone-related diseases. Firstly, we underscore the significance of MSC-EVs in facilitating crosstalk between cells within the skeletal environment. Secondly, we highlight strategies of functional-modified EVs for treating bone-related diseases. We explore the pretreatment of stem cells using various biotechniques to enhance the properties of resulting EVs, as well as diverse approaches to modify MSC-EVs for targeted delivery and controlled release. Finally, we address the challenges and opportunities for further research on MSC-EVs in bone-related diseases.

M2 macrophage-derived exosomes carry miR-142-3p to restore the differentiation balance of irradiated BMMSCs by targeting TGF-β1

Radiotherapy is essential to cancer treatment, while it inevitably injures surrounding normal tissues, and bone tissue is one of the most common sites prone to irradiation. Bone marrow mesenchymal stem cells (BMMSCs) are sensitive to irradiation and the irradiated dysfunction of BMMSCs may be closely related to irradiation-induced bone damage. Macropahges play important role in regulating stem cell function, bone metabolic balance and irradiation response, but the effects of macrophages on irradiated BMMSCs are still unclear. This study aimed to investigate the role of macrophages and macrophage-derived exosomes in restoring irradiated BMMSCs function. The effects of macrophage conditioned medium (CM) and macrophage-derived exosomes on osteogenic and fibrogenic differentiation capacities of irradiated BMMSCs were detected. The key microribonucleic acids (miRNAs) and targeted proteins in exosomes were also determined. The results showed that irradiation significantly inhibited the proliferation of BMMSCs, and caused differentiation imbalance of BMMSCs, with decreased osteogenic differentiation and increased fibrogenic differentiation. M2 macrophage-derived exosomes (M2D-exos) inhibited the fibrogenic differentiation and promoted the osteogenic differentiation of irradiated BMMSCs. We identified that miR-142-3p was significantly overexpressed in M2D-exos and irradiated BMMSCs treated with M2D-exos. After inhibition of miR-142-3p in M2 macrophage, the effects of M2D-exos on irradiated BMMSCs differentiation were eliminated. Furthermore, transforming growth factor beta 1 (TGF-β1), as a direct target of miR-142-3p, was significantly decreased in irradiated BMMSCs treated with M2D-exos. This study indicated that M2D-exos could carry miR-142-3p to restore the differentiation balance of irradiated BMMSCs by targeting TGF-β1. These findings pave a new way for promising and cell-free method to treat irradiation-induced bone damage.

Role of macrophages and their exosomes in orthopedic diseases

Exosomes are vesicles with a lipid bilayer structure that carry various active substances, such as proteins, DNA, non-coding RNA, and nucleic acids; these participate in the immune response, tissue formation, and cell communication. Owing to their low immunogenicity, exosomes play a key role in regulating the skeletal immune environment. Macrophages are important immune cells that swallow various cellular and tissue fragments. M1-like and M2-like macrophages differentiate to play pro-inflammatory, anti-inflammatory, and repair roles following stimulation. In recent years, the increase in the population base and the aging of the population have led to a gradual rise in orthopedic diseases, placing a heavy burden on the social medical system and making it urgent to find effective solutions. Macrophages and their exosomes have been demonstrated to be closely associated with the pathogenesis and prognosis of orthopedic diseases. An in-depth understanding of their mechanisms of action and the interaction between them will be helpful for the future clinical treatment of orthopedic diseases. This review focuses on the mechanisms of action, diagnosis, and treatment of orthopedic diseases involving macrophages and their exosomes, including fracture healing, diabetic bone damage, osteosarcoma, and rheumatoid arthritis. In addition, we discuss the prospects and major challenges faced by macrophages and their exosomes in clinical practice.

Tantalum Particles Promote M2 Macrophage Polarization and Regulate Local Bone Metabolism via Macrophage-Derived Exosomes Influencing the Fates of BMSCs

In this study, the regulatory role and mechanisms of tantalum (Ta) particles in the bone tissue microenvironment are explored. Ta particle deposition occurs in both clinical samples and animal tissues following porous Ta implantation. Unlike titanium (Ti) particles promoting M1 macrophage (Mϕ) polarization, Ta particles regulating calcium signaling pathways and promoting M2 Mϕ polarization. Ta-induced M2 Mϕ enhances bone marrow-derived mesenchymal stem cells (BMSCs) proliferation, migration, and osteogenic differentiation through exosomes (Exo) by upregulating miR-378a-3p/miR-221-5p and downregulating miR-155-5p/miR-212-5p. Ta particles suppress the pro-inflammatory and bone resorption effects of Ti particles in vivo and in vitro. In a rat femoral condyle bone defect model, artificial bone loaded with Ta particles promotes endogenous Mϕ polarization toward M2 differentiation at the defect site, accelerating bone repair. In conclusion, Ta particles modulate Mϕ polarization toward M2 and influence BMSCs osteogenic capacity through Exo secreted by M2 Mϕ, providing insights for potential bone repair applications.

Magnesium-containing bioceramics stimulate exosomal miR-196a-5p secretion to promote senescent osteogenesis through targeting Hoxa7/MAPK signaling axis

Stem cell senescence is characterized by progressive functional dysfunction and secretory phenotypic changes including decreased proliferation, dysfunction of osteogenic and angiogenic differentiation, increased secretion of the senescence-associated secretory phenotype (SASP), which bring difficulties for bone repair. Rescuing or delaying senescence of aged bone marrow mesenchymal stem cells (O-BMSCs) was considered as effective strategy for bone regeneration in aging microenvironment. Magnesium (Mg) ion released from bioceramics was reported to facilitate bone regeneration via enhancing osteogenesis and alleviating senescence. In this study, Akermanite biocreamics (Akt) containing Mg ion as a model was demonstrated to promote osteogenesis and angiogenesis effects of O-BMSCs by activating the MAPK signaling pathway in vitro. Moreover, the enhanced osteogenesis effects might be attributed to enhanced Mg-containing Akt-mediated exosomal miR-196a-5p cargo targeting Hoxa7 and activation of MAPK signaling pathway. Furthermore, the in vivo study confirmed that 3D-printed porous Mg-containing Akt scaffolds effectively increased bone regeneration in cranial defects of aged rats. The current results indicated that the exosomal-miR-196a-5p/Hoxa7/MAPK signaling axis might be the potential mechanism underlying Akt-mediated osteogenesis. The exosome-meditaed therapy stimulated by the released Mg ion contained in Akt biocreamics or other biomaterials might serve as a candidate strategy for bone repair in aged individuals.

Multifunctional DNA-Based Hydrogel Promotes Diabetic Alveolar Bone Defect Reconstruction

Diabetic alveolar bone defect (DABD) causes persistent bacterial infection, prolonged inflammation, and delayed bone healing, making it a considerable clinical challenge. In this study, by integrating silver nanoclusters (AgNCs) and M2 macrophage-derived extracellular vesicles (M2EVs), a multifunctional DNA-based hydrogel, called Agevgel, is developed with antibacterial, anti-inflammatory, immunomodulatory, and osteogenic properties to promote DABD rebuilding. AgNCs are tightly embedded into the DNA scaffolds and exhibit effective anti-bacterial activity, while immunomodulatory M2EVs are encapsulated within the shape-variable DNA scaffolds and exhibit potent anti-inflammatory and osteogenic properties. The results reveal that Agevgel effectively prolongs the local retention time and bioactivity of M2EVs in vivo. In particular, the sustained release of M2EVs can last for at least 7 days when applying Agevgel to DABD. Compared to free M2EVs or Aggel (AgNCs encapsulated within the DNA hydrogel) treatments, the Agevgel treatment accelerates the defect healing rate of alveolar bone and dramatically improves the trabecular architecture. Mechanistically, Agevgel plays a key role in regulating macrophage polarization and promoting the expression of proliferative and osteogenic factors. In summary, Agevgel provides a comprehensive treatment strategy for DABD with a great clinical translational value, highlighting the application of DNA hydrogels as an ideal bioscaffolds for periodontal diseases.

Mogroside V alleviates inflammation response by modulating miR-21-5P/SPRY1 axis

Mogroside V (MV) is a natural sweetener extracted from the edible plant Siraitia grosvenorii that possesses anti-inflammatory bioactivity. It has been reported that microRNAs (miRNAs) play an important role in the inflammation response suppression by natural agents. However, whether the anti-inflammation effect of mogroside V is related to miRNAs and the underlying mechanism remains unclear. Our study aimed to identify the key miRNAs important for the anti-inflammation effect of MV and reveal its underlying mechanisms. Our results showed that MV effectively alleviated lung inflammation in ovalbumin-induced (OVA-induced) asthmatic mice. miRNA-seq and mRNA-seq combined analysis identified miR-21-5p as an important miRNA for the inflammation inhibition effect of MV and it predicted SPRY1 to be a target gene of miR-21-5p. We found that MV significantly inhibited the production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-2 (IL-2), interleukin-6 (IL-6), and nitric oxide (NO), as well as the protein expression of p-P65/P65, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS) in OVA-induced asthmatic mice and LPS-treated RAW 264.7 cells. Moreover, the release of ROS increased in LPS-stimulated RAW 264.7 cells but was mitigated by MV pretreatment. In the meantime, the expression of miR-21-5p was decreased by MV, leading to an increase in the expression of SPRY1 in RAW 264.7 cells. Furthermore, miR-21-5p overexpression or SPRY1 knockdown reversed MV's protective effect on inflammatory responses. Conversely, miR-21-5p inhibition or SPRY1 overexpression enhanced MV's effect on inflammatory responses in LPS-exposed RAW 264.7 cells. Therefore, the significant protective effect of mogroside V on inflammation response is related to the downregulation of miR-21-5p and upregulation of SPRY1 in vitro and in vivo, MiR-21-5p/SPRY1 may be novel therapeutic targets of MV for anti-inflammation treatment.

Multifunctional Exosomes Derived from M2 Macrophages with Enhanced Odontogenesis, Neurogenesis and Angiogenesis for Regenerative Endodontic Therapy: An In Vitro and In Vivo Investigation

INTRODUCTION

Exosomes derived from M2 macrophages (M2-Exos) exhibit tremendous potential for inducing tissue repair and regeneration. Herein, this study was designed to elucidate the biological roles of M2-Exos in regenerative endodontic therapy (RET) compared with exosomes from M1 macrophages (M1-Exos).

METHODS

The internalization of M1-Exos and M2-Exos by dental pulp stem cells (DPSCs) and human umbilical vein endothelial cells (HUVECs) was detected by uptake assay. The effects of M1-Exos and M2-Exos on DPSC and HUVEC behaviors, including migration, proliferation, odonto/osteogenesis, neurogenesis, and angiogenesis were determined in vitro. Then, Matrigel plugs incorporating M2-Exos were transplanted subcutaneously into nude mice. Immunostaining for vascular endothelial growth factor (VEGF) and CD31 was performed to validate capillary-like networks.

RESULTS

M1-Exos and M2-Exos were effectively absorbed by DPSCs and HUVECs. Compared with M1-Exos, M2-Exos considerably facilitated the proliferation and migration of DPSCs and HUVECs. Furthermore, M2-Exos robustly promoted ALP activity, mineral nodule deposition, and the odonto/osteogenic marker expression of DPSCs, indicating the powerful odonto/osteogenic potential of M2-Exos. In sharp contrast with M1-Exos, which inhibited the neurogenic capacity of DPSCs, M2-Exos contributed to a significantly augmented expression of neurogenic genes and the stronger immunostaining of Nestin. Consistent with remarkably enhanced angiogenic markers and tubular structure formation in DPSCs and HUVECs in vitro, the employment of M2-Exos gave rise to more abundant vascular networks, dramatically higher VEGF expression, and widely spread CD31+ tubular lumens in vivo, supporting the enormous pro-angiogenic capability of M2-Exos.

CONCLUSIONS

The multifaceted roles of M2-Exos in ameliorating DPSC and HUVEC functions potentially contribute to complete functional pulp-dentin complex regeneration.

Non-bone-derived exosomes: a new perspective on regulators of bone homeostasis

Accumulating evidence indicates that exosomes help to regulate bone homeostasis. The roles of bone-derived exosomes have been well-described; however, recent studies have shown that some non-bone-derived exosomes have better bone targeting ability than bone-derived exosomes and that their performance as a drug delivery vehicle for regulating bone homeostasis may be better than that of bone-derived exosomes, and the sources of non-bone-derived exosomes are more extensive and can thus be better for clinical needs. Here, we sort non-bone-derived exosomes and describe their composition and biogenesis. Their roles and specific mechanisms in bone homeostasis and bone-related diseases are also discussed. Furthermore, we reveal obstacles to current research and future challenges in the practical application of exosomes, and we provide potential strategies for more effective application of exosomes for the regulation of bone homeostasis and the treatment of bone-related diseases. Video Abstract.

The role and applications of extracellular vesicles in osteoporosis

Osteoporosis is a widely observed condition characterized by the systemic deterioration of bone mass and microarchitecture, which increases patient susceptibility to fragile fractures. The intricate mechanisms governing bone homeostasis are substantially impacted by extracellular vesicles (EVs), which play crucial roles in both pathological and physiological contexts. EVs derived from various sources exert distinct effects on osteoporosis. Specifically, EVs released by osteoblasts, endothelial cells, myocytes, and mesenchymal stem cells contribute to bone formation due to their unique cargo of proteins, miRNAs, and cytokines. Conversely, EVs secreted by osteoclasts and immune cells promote bone resorption and inhibit bone formation. Furthermore, the use of EVs as therapeutic modalities or biomaterials for diagnosing and managing osteoporosis is promising. Here, we review the current understanding of the impact of EVs on bone homeostasis, including the classification and biogenesis of EVs and the intricate regulatory mechanisms of EVs in osteoporosis. Furthermore, we present an overview of the latest research progress on diagnosing and treating osteoporosis by using EVs. Finally, we discuss the challenges and prospects of translational research on the use of EVs in osteoporosis.

M2 exosomes modified by hydrogen sulfide promoted bone regeneration by moesin mediated endocytosis

Bone defects caused by trauma or tumor led to high medical costs and poor life quality for patients. The exosomes, micro vesicles of 30-150 nm in diameter, derived from macrophages manipulated bone regeneration. However, the role of hydrogen sulfide (H2S) in the biogenesis and function of exosomes and its effects on bone regeneration remains elusive. In this study, we used H2S slow releasing donor GYY4137 to stimulate macrophages and found that H2S promoted the polarization of M2 macrophages to increase bone regeneration of MSCs in vitro and in vivo. Moreover, we developed the H2S pre-treated M2 macrophage exosomes and found these exosomes displayed significantly higher capacity to promote bone regeneration in calvarial bone defects by re-establishing the local immune microenvironment. Mechanically, H2S treatment altered the protein profile of exosomes derived from M2 macrophages. One of the significantly enriched exosomal proteins stimulated by H2S, moesin protein, facilitated the exosomes endocytosis into MSCs, leading to activated the β-catenin signaling pathway to promote osteogenic differentiation of MSCs. In summary, H2S pretreated M2 exosomes promoted the bone regeneration of MSCs via facilitating exosomes uptake by MSCs and activate β-catenin signaling pathway. This study not only provides new strategies for promoting bone regeneration, but also provides new insights for the effect and mechanism of exosomes internalization.

Temporal Immunomodulation via Wireless Programmed Electric Cues Achieves Optimized Diabetic Bone Regeneration

Mimicking the temporal pattern of biological behaviors during the natural repair process is a promising strategy for biomaterial-mediated tissue regeneration. However, precise regulation of dynamic cell behaviors allocated in a microenvironment post-implantation remains challenging until now. Here, remote tuning of electric cues is accomplished by wireless ultrasound stimulation (US) on an electroactive membrane for bone regeneration under a diabetic background. Programmable electric cues mediated by US from the piezoelectric membrane achieve the temporal regulation of macrophage polarization, satisfying the pattern of immunoregulation during the natural healing process and effectively promoting diabetic bone repair. Mechanistic insight reveals that the controllable decrease in AKT2 expression and phosphorylation could explain US-mediated macrophage polarization. This study exhibits a strategy aimed at precisely biosimulating the temporal regenerative pattern by controllable and programmable electric output for optimized diabetic tissue regeneration and provides basic insights into bionic design-based precision medicine achieved by intelligent and external field-responsive biomaterials.

Cellular and Molecular Connections Between Bone Fracture Healing and Exosomes

Fracture healing is a multifaceted process that requires various phases and intercellular interactions. In recent years, investigations have been conducted to assess the feasibility of utilizing exosomes, small extracellular vesicles (EVs), to enhance and accelerate the healing process. Exosomes serve as a cargo transport platform, facilitating intercellular communication, promoting the presentation of antigens to dendritic cells, and stimulating angiogenesis. Exosomes have a special structure that gives them a special function, especially in the healing process of bone injuries. This article provides an overview of cellular and molecular processes associated with bone fracture healing, as well as a survey of existing exosome research in this context. We also discuss the potential use of exosomes in fracture healing, as well as the obstacles that must be overcome to make this a viable clinical practice.

M2 macrophage-derived exosomes promote diabetic fracture healing by acting as an immunomodulator

Diabetes mellitus is a chronically inflamed disease that predisposes to delayed fracture healing. Macrophages play a key role in the process of fracture healing by undergoing polarization into either M1 or M2 subtypes, which respectively exhibit pro-inflammatory or anti-inflammatory functions. Therefore, modulation of macrophage polarization to the M2 subtype is beneficial for fracture healing. Exosomes perform an important role in improving the osteoimmune microenvironment due to their extremely low immunogenicity and high bioactivity. In this study, we extracted the M2-exosomes and used them to intervene the bone repair in diabetic fractures. The results showed that M2-exosomes significantly modulate the osteoimmune microenvironment by decreasing the proportion of M1 macrophages, thereby accelerating diabetic fracture healing. We further confirmed that M2-exosomes induced the conversion of M1 macrophages into M2 macrophages by stimulating the PI3K/AKT pathway. Our study offers a fresh perspective and a potential therapeutic approach for M2-exosomes to improve diabetic fracture healing.

rFSAV promotes Staphylococcus aureus-infected bone defect healing via IL-13- mediated M2 macrophage polarization

Staphylococcus aureus (S. aureus) contamination commonly occurs in orthopedic internal fixation operations, leading to a delayed healing of the defected bone tissue. However, antibiotic treatments are ineffective in dealing with S. aureus bone infections due to the rise in multiple antimicrobial resistances. Here, we reported the protective effects of a recombinant five-antigen S. aureus vaccine (rFSAV) in an S. aureus infected bone defect model. In this study, we found the number of M2 macrophages markedly increased in the defect site and played a critical role in the healing of defected bone mediated by rFSAV. Mechanistically, rFSAV mediated increased level of IL-13 in bone defect site predominant M2 macrophage polarization. In summary, our study reveals a key role of M2 macrophage polarization in the bone regeneration process in S. aureus infection induced bone defect, which provide a promising application of rFSAV for the treatment of bone infection for orthopedic applications.

Harnessing Stem Cell-Derived Extracellular Vesicles for the Regeneration of Degenerative Bone Conditions

Degenerative bone disorders such as intervertebral disc degeneration (IVDD), osteoarthritis (OA), and osteoporosis (OP) pose significant health challenges for aging populations and lack effective treatment options. The field of regenerative medicine holds promise in addressing these disorders, with a focus on utilizing extracellular vesicles (EVs) derived from stem cells as an innovative therapeutic approach. EVs have shown great potential in stimulating biological responses, making them an attractive candidate for rejuvenating degenerative bone disorders. However, a comprehensive review summarizing the current state of this field and providing a clear assessment of EV-based therapies in degenerative bone disorders is currently deficient. In this review, we aim to fill the existing gap by outlining the current knowledge on the role of EVs derived from different types of stem cells, such as mesenchymal stem cells, embryonic stem cells, and induced pluripotent stem cells, in bone regeneration. Furthermore, we discuss the therapeutic potential of EV-based treatments for IVDD, OA, and OP. By substantiating the use of stem cell-derived EVs, we highlight their promising potential as a cell-free strategy to improve degenerative bone disorders.

M2 macrophage-derived exosomal miR-486-5p influences the differentiation potential of bone marrow mesenchymal stem cells and osteoporosis

BACKGROUND

An imbalance between osteogenesis and adipogenesis in bone marrow mesenchymal stem cells (BMMSCs) can cause osteoporosis. Macrophage-derived exosomes (MD-Exos) and microRNAs (miRNAs) enriched in exosomes participate in the differentiation of BMMSCs.

METHODS

Bioinformatics methods were used to analyze differentially expressed miRNAs. We cocultured M2 macrophages and BMMSCs to examine the biological function of exosomal microRNA-486-5p (miR-486-5p) on BMMSCs differentiation. Gain-of-function experiments related to osteogenesis were designed to investigate the effects of exosomes carrying miR-486-5p on an ovariectomized (OVX) mice model and the direct impact of miR-486-5p on BMMSCs. A dual luciferase experiment was performed to demonstrate the target gene of miR-486-5p.

RESULTS

Bioinformatics analysis identified high expression of miRNA-486 in M2 macrophage-derived exosomes (M2D-Exos). The in vitro results demonstrated that M2 macrophage-derived exosomal miR-486-5p enhanced osteogenic capacity but inhibited the adipogenesis of BMMSCs. The direct effect of miR-486-5p on BMMSCs showed the same effects. Animal experiments revealed that exosomal miR-486-5p rescued bone loss of OVX mice. SMAD2 was characterized as a target gene of miR-486-5p. Pathway analysis showed that M2 macrophage-derived exosomal miR-486-5p stimulated osteogenic differentiation via the TGF-β/SMAD2 signalling pathway.

CONCLUSIONS

Taken together, M2 macrophage-derived exosomal miR-486-5p influences the differentiation potential of BMMSCs through the miR-486-5p/SMAD2/TGF-β signalling pathway and osteoporosis.

Harnessing exosomes as cutting-edge drug delivery systems for revolutionary osteoarthritis therapy

Exosomes, remarkable extracellular vesicles, have emerged as an advanced frontier in intercellular communication. This remarkable capacity positions them as promising contenders in drug delivery systems (DDSs) for osteoarthritis (OA) therapy, capitalizing on their inherent biocompatibility, stability, and minimal immunogenicity. In this comprehensive review, we summarize the emerging developments surrounding exosome-based DDSs for OA therapy. Focusing on exosome origins, we meticulously explore the diverse sources contributing to their production, including invaluable stem cells, immune cells, and an array of other cell types. In addition, we unravel the underlying mechanisms of action that govern these exosome-borne therapeutics, illuminating the intricate interplay between exosomes and recipient cells. In summary, this review highlights the present challenges that permeate exosome-based DDSs for OA therapy. Through an in-depth exploration of the intricacies within this emerging field, this review aims to shed light on the future direction of exosome-based DDSs in OA. It serves as a bridge for fostering collaboration and collective efforts in reshaping the treatment landscape of OA.

MicroRNA-21a-5p-modified macrophage exosomes as natural nanocarriers promote bone regeneration by targeting GATA2

Bone immune responses based on macrophages are critical in the osteogenesis of bone abnormalities. In general, M2 macrophage facilitate the promotion of osteogenesis, as well, M1 macrophage play an important role in early bone healing, as confirmed by previous studies. However, it is not clear how M1 macrophage are involved in the bone immune response. MiR-21a-5p is a highly expressed microRNA in M1 macrophage in contrast to M2. Therefore, the current work sought to ascertain the influence of M1 macrophage on bone healing via exosomal miR-21a-5p and the probable mechanism. We discovered that injecting M1 macrophage exosomes overexpressing miR-21a-5p into bone defect locations enhanced bone regeneration in vivo. Furthermore, by directly targeting GATA2, miR-21a-5p accelerated MC3T3-E1 osteogenic differentiation. Our findings showed that exosomal miR-21a-5p from M1 macrophage may be transported to osteoblasts and target GATA2 to enhance bone defect healing.

Macrophages-bone marrow mesenchymal stem cells crosstalk in bone healing

Bone healing is associated with many orthopedic conditions, including fractures and osteonecrosis, arthritis, metabolic bone disease, tumors and periprosthetic particle-associated osteolysis. How to effectively promote bone healing has become a keen topic for researchers. The role of macrophages and bone marrow mesenchymal stem cells (BMSCs) in bone healing has gradually come to light with the development of the concept of osteoimmunity. Their interaction regulates the balance between inflammation and regeneration, and when the inflammatory response is over-excited, attenuated, or disturbed, it results in the failure of bone healing. Therefore, an in-depth understanding of the function of macrophages and bone marrow mesenchymal stem cells in bone regeneration and the relationship between the two could provide new directions to promote bone healing. This paper reviews the role of macrophages and bone marrow mesenchymal stem cells in bone healing and the mechanism and significance of their interaction. Several new therapeutic ideas for regulating the inflammatory response in bone healing by targeting macrophages and bone marrow mesenchymal stem cells crosstalk are also discussed.

Stimulating factors for regulation of osteogenic and chondrogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs), distributed in many tissues in the human body, are multipotent cells capable of differentiating in specific directions. It is usually considered that the differentiation process of MSCs depends on specialized external stimulating factors, including cell signaling pathways, cytokines, and other physical stimuli. Recent findings have revealed other underrated roles in the differentiation process of MSCs, such as material morphology and exosomes. Although relevant achievements have substantially advanced the applicability of MSCs, some of these regulatory mechanisms still need to be better understood. Moreover, limitations such as long-term survival in vivo hinder the clinical application of MSCs therapy. This review article summarizes current knowledge regarding the differentiation patterns of MSCs under specific stimulating factors.

Bioengineering extracellular vesicles: smart nanomaterials for bone regeneration

In the past decade, extracellular vesicles (EVs) have emerged as key regulators of bone development, homeostasis and repair. EV-based therapies have the potential to circumnavigate key issues hindering the translation of cell-based therapies including functional tissue engraftment, uncontrolled differentiation and immunogenicity issues. Due to EVs' innate biocompatibility, low immunogenicity, and high physiochemical stability, these naturally-derived nanoparticles have garnered growing interest as potential acellular nanoscale therapeutics for a variety of diseases. Our increasing knowledge of the roles these cell-derived nanoparticles play, has made them an exciting focus in the development of novel pro-regenerative therapies for bone repair. Although these nano-sized vesicles have shown promise, their clinical translation is hindered due to several challenges in the EV supply chain, ultimately impacting therapeutic efficacy and yield. From the biochemical and biophysical stimulation of parental cells to the transition to scalable manufacture or maximising vesicles therapeutic response in vivo, a multitude of techniques have been employed to improve the clinical efficacy of EVs. This review explores state of the art bioengineering strategies to promote the therapeutic utility of vesicles beyond their native capacity, thus maximising the clinical potential of these pro-regenerative nanoscale therapeutics for bone repair.

Differential Expression of Non-Coding RNAs in Stem Cell Development and Therapeutics of Bone Disorders

Stem cells' self-renewal and multi-lineage differentiation are regulated by a complex network consisting of signaling factors, chromatin regulators, transcription factors, and non-coding RNAs (ncRNAs). Diverse role of ncRNAs in stem cell development and maintenance of bone homeostasis have been discovered recently. The ncRNAs, such as long non-coding RNAs, micro RNAs, circular RNAs, small interfering RNA, Piwi-interacting RNAs, etc., are not translated into proteins but act as essential epigenetic regulators in stem cells' self-renewal and differentiation. Different signaling pathways are monitored efficiently by the differential expression of ncRNAs, which function as regulatory elements in determining the fate of stem cells. In addition, several species of ncRNAs could serve as potential molecular biomarkers in early diagnosis of bone diseases, including osteoporosis, osteoarthritis, and bone cancers, ultimately leading to the development of new therapeutic strategies. This review aims to explore the specific roles of ncRNAs and their effective molecular mechanisms in the growth and development of stem cells, and in the regulation of osteoblast and osteoclast activities. Furthermore, we focus on and explore the association of altered ncRNA expression with stem cells and bone turnover.

Exosomal Lnc NEAT1 from endothelial cells promote bone regeneration by regulating macrophage polarization via DDX3X/NLRP3 axis

BACKGROUND

Bone regeneration is a complex procedure that involves an interaction between osteogenesis and inflammation. Macrophages in the microenvironment are instrumental in bone metabolism. Amount evidence have revealed that exosomes transmitting lncRNA is crucial nanocarriers for cellular interactions in various biotic procedures, especially, osteogenesis. However, the underlying mechanisms of the regulatory relationship between the exosomes and macrophages are awaiting clarification. In the present time study, we aimed to explore the roles of human umbilical vein endothelial cells (HUVECs)-derived exosomes carrying nuclear enrichment enriched transcript 1 (NEAT1) in the osteogenesis mediated by M2 polarized macrophages and elucidate the underlying mechanisms.

RESULTS

We demonstrated HUVECs-derived exosomes expressing NEAT1 significantly enhanced M2 polarization and attenuated LPS-induced inflammation in vitro. Besides, the conditioned medium from macrophages induced by the exosomes indirectly facilitated the migration and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). Mechanically, Exos carrying NEAT1 decreased remarkably both expression of dead-box helicase 3X-linked (DDX3X) and nod-like receptor protein 3 (NLRP3). The level of NLRP3 protein increased significantly after RAW264.7 cells transfected with DDX3X overexpression plasmid. Additionally, the knockdown of NEAT1 in exosomes partially counteracted the aforementioned effect of Exos. The results of air pouch rat model demonstrated that HUVECs-derived exosomes increased anti-inflammatory cytokines (IL-10) and decreased pro-inflammatory cytokines (IL-1β and IL-6) significantly in vivo, contributing to amelioration of LPS-induced inflammation. Afterwards, we further confirmed that the HUVECs-derived exosomes encapsulated in alginate/gelatin methacrylate (GelMA) interpenetrating polymer network (IPN) hydrogels could promote the bone regeneration, facilitate the angiogenesis, increase the infiltration of M2 polarized macrophages as well as decrease NLRP3 expression in the rat calvarial defect model.

CONCLUSIONS

HUVECs-derived exosomes enable transmitting NEAT1 to alleviate inflammation by inducing M2 polarization of macrophages through DDX3X/NLRP3 regulatory axis, which finally contributes to osteogenesis with the aid of alginate/GelMA IPN hydrogels in vivo. Thus, our study provides insights in bone healing with the aid of HUVECs-derived exosomes-encapsulated composite hydrogels, which exhibited potential towards the use of bone tissue engineering in the foreseeable future.

Hyaluronic acid-based hydrogels: As an exosome delivery system in bone regeneration

Exosomes are extracellular vesicles (EVs) containing various ingredients such as DNA, RNA, lipids and proteins, which play a significant role in intercellular communication. Numerous studies have demonstrated the important role of exosomes in bone regeneration through promoting the expression of osteogenic-related genes and proteins in mesenchymal stem cells. However, the low targeting ability and short circulating half-life of exosomes limited their clinical application. In order to solve those problems, different delivery systems and biological scaffolds have been developed. Hydrogel is a kind of absorbable biological scaffold composed of three-dimensional hydrophilic polymers. It not only has excellent biocompatibility and superior mechanical strength but can also provide a suitable nutrient environment for the growth of the endogenous cells. Thus, the combination between exosomes and hydrogels can improve the stability and maintain the biological activity of exosomes while achieving the sustained release of exosomes in the bone defect sites. As an important component of the extracellular matrix (ECM), hyaluronic acid (HA) plays a critical role in various physiological and pathological processes such as cell differentiation, proliferation, migration, inflammation, angiogenesis, tissue regeneration, wound healing and cancer. In recent years, hyaluronic acid-based hydrogels have been used as an exosome delivery system for bone regeneration and have displayed positive effects. This review mainly summarized the potential mechanism of HA and exosomes in promoting bone regeneration and the application prospects and challenges of hyaluronic acid-based hydrogels as exosome delivery devices in bone regeneration.

The Applications and Potentials of Extracellular Vesicles from Different Cell Sources in Periodontal Regeneration

Periodontitis is a chronic infectious disease worldwide that can cause damage to periodontal supporting tissues including gingiva, bone, cementum and periodontal ligament (PDL). The principle for the treatment of periodontitis is to control the inflammatory process. Achieving structural and functional regeneration of periodontal tissues is also essential and remains a major challenge. Though many technologies, products, and ingredients were applied in periodontal regeneration, most of the strategies have limited outcomes. Extracellular vesicles (EVs) are membranous particles with a lipid structure secreted by cells, containing a large number of biomolecules for the communication between cells. Numerous studies have demonstrated the beneficial effects of stem cell-derived EVs (SCEVs) and immune cell-derived EVs (ICEVs) on periodontal regeneration, which may be an alternative strategy for cell-based periodontal regeneration. The production of EVs is highly conserved among humans, bacteria and plants. In addition to eukaryocyte-derived EVs (CEVs), a growing body of literature suggests that bacterial/plant-derived EVs (BEVs/PEVs) also play an important role in periodontal homeostasis and regeneration. The purpose of this review is to introduce and summarize the potential therapeutic values of BEVs, CEVs and PEVs in periodontal regeneration, and discuss the current challenges and prospects for EV-based periodontal regeneration.

Mechanical force induces macrophage-derived exosomal UCHL3 promoting bone marrow mesenchymal stem cell osteogenesis by targeting SMAD1

BACKGROUND

Orthodontic tooth movement (OTM), a process of alveolar bone remodelling, is induced by mechanical force and regulated by local inflammation. Bone marrow-derived mesenchymal stem cells (BMSCs) play a fundamental role in osteogenesis during OTM. Macrophages are mechanosensitive cells that can regulate local inflammatory microenvironment and promote BMSCs osteogenesis by secreting diverse mediators. However, whether and how mechanical force regulates osteogenesis during OTM via macrophage-derived exosomes remains elusive.

RESULTS

Mechanical stimulation (MS) promoted bone marrow-derived macrophage (BMDM)-mediated BMSCs osteogenesis. Importantly, when exosomes from mechanically stimulated BMDMs (MS-BMDM-EXOs) were blocked, the pro-osteogenic effect was suppressed. Additionally, compared with exosomes derived from BMDMs (BMDM-EXOs), MS-BMDM-EXOs exhibited a stronger ability to enhance BMSCs osteogenesis. At in vivo, mechanical force-induced alveolar bone formation was impaired during OTM when exosomes were blocked, and MS-BMDM-EXOs were more effective in promoting alveolar bone formation than BMDM-EXOs. Further proteomic analysis revealed that ubiquitin carboxyl-terminal hydrolase isozyme L3 (UCHL3) was enriched in MS-BMDM-EXOs compared with BMDM-EXOs. We went on to show that BMSCs osteogenesis and mechanical force-induced bone formation were impaired when UCHL3 was inhibited. Furthermore, mothers against decapentaplegic homologue 1 (SMAD1) was identified as the target protein of UCHL3. At the mechanistic level, we showed that SMAD1 interacted with UCHL3 in BMSCs and was downregulated when UCHL3 was suppressed. Consistently, overexpression of SMAD1 rescued the adverse effect of inhibiting UCHL3 on BMSCs osteogenesis.

CONCLUSIONS

This study suggests that mechanical force-induced macrophage-derived exosomal UCHL3 promotes BMSCs osteogenesis by targeting SMAD1, thereby promoting alveolar bone formation during OTM.

Circulating MiRNA-21-enriched extracellular vesicles promote bone remodeling in traumatic brain injury patients

Fracture combined with traumatic brain injury (TBI) is one of the most common and serious types of compound trauma in the clinic and is characterized by dysfunction of cellular communication in injured organs. Our prior studies found that TBI was capable of enhancing fracture healing in a paracrine manner. Exosomes (Exos), as small extracellular vesicles, are important paracrine vehicles for noncell therapy. However, whether circulating Exos derived from TBI patients (TBI-Exos) regulate the prohealing effects of fractures remains unclear. Thus, the present study aimed to explore the biological effects of TBI-Exos on fracture healing and reveal the potential molecular mechanism. TBI-Exos were isolated by ultracentrifugation, and the enriched miR-21-5 p was identified by qRT‒PCR analysis. The beneficial effects of TBI-Exos on osteoblastic differentiation and bone remodeling were determined by a series of in vitro assays. Bioinformatics analyses were conducted to identify the potential downstream mechanisms of the regulatory effect of TBI-Exos on osteoblasts. Furthermore, the role of the potential signaling pathway of TBI-Exos in mediating the osteoblastic activity of osteoblasts was assessed. Subsequently, a murine fracture model was established, and the effect of TBI-Exos on bone modeling was demonstrated in vivo. TBI-Exos can be internalized by osteoblasts, and in vitro, suppression of SMAD7 promoted osteogenic differentiation, whereas knockdown of miR-21-5 p in TBI-Exos strongly inhibited this bone-beneficial effect. Similarly, our results confirmed that preinjection of TBI-Exos led to enhanced bone formation, whereas knockdown of exosomal miR-21-5 p substantially impaired this bone-beneficial effect in vivo.

Exosomes Derived from Adipose Stem Cells Enhance Bone Fracture Healing via the Activation of the Wnt3a/β-Catenin Signaling Pathway in Rats with Type 2 Diabetes Mellitus

Nonunion and delayed union are common complications of diabetes mellitus that pose a serious health threat to people. There are many approaches that have been used to improve bone fracture healing. Recently, exosomes have been regarded as promising medical biomaterials for improving fracture healing. However, whether exosomes derived from adipose stem cells can promote bone fracture healing in diabetes mellitus remains unclear. In this study, adipose stem cells (ASCs) and exosomes derived from adipose stem cells (ASCs-exos) are isolated and identified. Additionally, we evaluate the in vitro and in vivo effects of ASCs-exos on the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and bone repair and the regeneration in a rat model of nonunion via Western blotting, immunofluorescence assay, ALP staining, alizarin red staining, radiographic examination and histological analysis. Compared with controls, ASCs-exos promoted BMSC osteogenic differentiation. Additionally, the results of Western blotting, radiographic examination and histological analysis show that ASCs-exos improve the ability for fracture repair in the rat model of nonunion bone fracture healing. Moreover, our results further proved that ASCs-exos play a role in activating the Wnt3a/β-catenin signaling pathway, which facilitates the osteogenic differentiation of BMSCs. All these results show that ASCs-exos enhance the osteogenic potential of BMSCs by activating the Wnt/β-catenin signaling pathway, and also facilitate the ability for bone repair and regeneration in vivo, which provides a novel direction for fracture nonunion in diabetes mellitus treatment.

Macrophages and Bone Remodeling

Bone remodeling in the adult skeleton facilitates the removal and replacement of damaged and old bone to maintain bone quality. Tight coordination of bone resorption and bone formation during remodeling crucially maintains skeletal mass. Increasing evidence suggests that many cell types beyond osteoclasts and osteoblasts support bone remodeling, including macrophages and other myeloid lineage cells. Herein, we discuss the origin and functions for macrophages in the bone microenvironment, tissue resident macrophages, osteomacs, as well as newly identified osteomorphs that result from osteoclast fission. We also touch on the role of macrophages during inflammatory bone resorption. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Dual-Targeted Nanodiscs Revealing the Cross-Talk between Osteogenic Differentiation of Mesenchymal Stem Cells and Macrophages

Ongoing research has highlighted the significance of the cross-play of macrophages and mesenchymal stem cells (MSCs). Lysine-specific demethylase 6B (KDM6B) has been shown to control osteogenic differentiation of MSCs by depleting trimethylated histone 3 lysine 27 (H3K27me3). However, to date, the role of KDM6B in bone marrow-derived macrophages (BMDMs) remains controversial. Here, a chromatin immunoprecipitation assay (ChIP) proved that KDM6B derived from osteogenic-induced BMSCs could bind to the promoter region of BMDMs' brain and muscle aryl hydrocarbon receptor nuclear translocator-like protein-1 (BMAL1) gene in a coculture system and activate BMAL1. Transcriptome sequencing and experiments in vitro showed that the overexpression of BMAL1 in BMDM could inhibit the TLR2/NF-κB signaling pathway, reduce pyroptosis, and decrease the M1/M2 ratio, thereby promoting osteogenic differentiation of BMSCs. Furthermore, bone and macrophage dual-targeted GSK-J4 (KDM6B inhibitor)-loaded nanodiscs were synthesized via binding SDSSD-apoA-1 peptide analogs (APA) peptide, which indirectly proved the critical role of KDM6B in osteogenesis in vivo. Overall, we demonstrated that KDM6B serves as a positive circulation trigger during osteogenic differentiation by decreasing the ratio of M1/M2 both in vitro and in vivo. Collectively, these results provide insight into basic research in the field of osteoporosis and bone repair.

The role of macrophages in fracture healing: a narrative review of the recent updates and therapeutic perspectives

Objective

This review addresses the latest advances in research on the role of macrophages in fracture healing, exploring their relationship with failures in bone consolidation and the perspectives for the development of advanced and innovative therapies to promote bone regeneration.

Background

The bone can fully restore its form and function after a fracture. However, the regenerative process of fracture healing is complex and is influenced by several factors, including macrophage activity. These cells have been found in the fracture site at all stages of bone regeneration, and their general depletion or the knockdown of receptors that mediate their differentiation, polarization, and/or function result in impaired fracture healing.

Methods

The literature search was carried out in the PubMed database, using combinations of the keywords "macrophage", "fracture healing, "bone regeneration", and "bone repair". Articles published within the last years (2017-2022) reporting evidence from in vivo long bone fracture healing experiments were included.

Conclusions

Studies published in the last five years on the role of macrophages in fracture healing strengthened the idea that what appears to be essential when it comes to a successful consolidation is the right balance between the M1/M2 populations, which have different but complementary roles in the process. These findings opened promising new avenues for the development of several macrophage-targeted therapies, including the administration of molecules and/or biomaterials intended to regulate macrophage differentiation and polarization, the local transplantation of macrophage precursors, and the use of exosomes to deliver signaling molecules that influence macrophage activities. However, more research is still warranted to better understand the diversity of macrophage phenotypes and their specific roles in each step of fracture healing and to decipher the key molecular mechanisms involved in the in vivo crosstalk between macrophages and other microenvironmental cell types, such as endothelial and skeletal stem/progenitor cells.

The potential therapeutic role of extracellular vesicles in critical-size bone defects: Spring of cell-free regenerative medicine is coming

In recent years, the incidence of critical-size bone defects has significantly increased. Critical-size bone defects seriously affect patients' motor functions and quality of life and increase the need for additional clinical treatments. Bone tissue engineering (BTE) has made great progress in repairing critical-size bone defects. As one of the main components of bone tissue engineering, stem cell-based therapy is considered a potential effective strategy to regenerate bone tissues. However, there are some disadvantages including phenotypic changes, immune rejection, potential tumorigenicity, low homing efficiency and cell survival rate that restrict its wider clinical applications. Evidence has shown that the positive biological effects of stem cells on tissue repair are largely mediated through paracrine action by nanostructured extracellular vesicles (EVs), which may overcome the limitations of traditional stem cell-based treatments. In addition to stem cell-derived extracellular vesicles, the potential therapeutic roles of nonstem cell-derived extracellular vesicles in critical-size bone defect repair have also attracted attention from scholars in recent years. Currently, the development of extracellular vesicles-mediated cell-free regenerative medicine is still in the preliminary stage, and the specific mechanisms remain elusive. Herein, the authors first review the research progress and possible mechanisms of extracellular vesicles combined with bone tissue engineering scaffolds to promote bone regeneration via bioactive molecules. Engineering modified extracellular vesicles is an emerging component of bone tissue engineering and its main progression and clinical applications will be discussed. Finally, future perspectives and challenges of developing extracellular vesicle-based regenerative medicine will be given. This review may provide a theoretical basis for the future development of extracellular vesicle-based biomedicine and provide clinical references for promoting the repair of critical-size bone defects.

Advances in the Study of Exosomes as Drug Delivery Systems for Bone-Related Diseases

Bone-related diseases are major problems and heavy burdens faced by modern society. Current clinical approaches for the treatment of these pathological conditions often lead to complications and have limited therapeutic efficacy. In this context, the development of nanotherapeutic platforms, such as extracellular vesicles, can improve the relevant therapeutic effects. In particular, exosomes are nano-sized, lipid bilayer extracellular vesicles secreted by many cells in mammals. Due to their innate capacity to transport materials-including proteins, lipids, and genes-among cells, as well as their innate attraction to target cells, they are considered to be a crucial medium for cell communication and are involved in a number of biological processes. Exosomes have been used as drug delivery vehicles in recent bone tissue engineering studies, in order to regulate bone homeostasis. However, the precise workings of the exosome regulatory network in maintaining bone homeostasis and its potential for treating bone injury remain unclear. To provide a fresh perspective for the study of exosomes in drug delivery and bone-related diseases, in this paper, we review recent studies on the roles of exosomes for drug delivery in bone homeostasis and bone-related diseases, as well as the composition and characteristics of exosomes and their regulatory roles in bone homeostasis and bone-related diseases, aiming to provide new ideas for the therapeutic application of exosomes in the treatment of bone-related diseases.

Extracellular vesicles derived from host and gut microbiota as promising nanocarriers for targeted therapy in osteoporosis and osteoarthritis

Osteoporosis (OP), a systemic bone disease that causes structural bone loss and bone mass loss, is often associated with fragility fractures. Extracellular vesicles (EVs) generated by mammalian and gut bacteria have recently been identified as important mediators in the intercellular signaling pathway that may play a crucial role in microbiota-host communication. EVs are tiny membrane-bound vesicles, which range in size from 20 to 400 nm. They carry a variety of biologically active substances across intra- and intercellular space. These EVs have developed as a promising research area for the treatment of OP because of their nanosized architecture, enhanced biocompatibility, reduced toxicity, drug loading capacity, ease of customization, and industrialization. This review describes the latest development of EVs derived from mammals and bacteria, including their internalization, isolation, biogenesis, classifications, topologies, and compositions. Additionally, breakthroughs in chemical sciences and the distinctive biological features of bacterial extracellular vesicles (BEVs) allow for the customization of modified BEVs for the therapy of OP. In conclusion, we give a thorough and in-depth summary of the main difficulties and potential future of EVs in the treatment of OP, as well as highlight innovative uses and choices for the treatment of osteoarthritis (OA).

Prognostic and therapeutic potential of microRNAs for fracture healing processes and non-union fractures: A systematic review

BACKGROUND

Approximately 10% of all bone fractures result in delayed fracture healing or non-union; thus, the identification of biomarkers and prognostic factors is of great clinical interest. MicroRNAs (miRNAs) are known to be involved in the regulation of the bone healing process and may serve as functional markers for fracture healing.

AIMS AND METHODS

This systematic review aimed to identify common miRNAs involved in fracture healing or non-union fractures using a qualitative approach. A systematic literature search was performed with the keywords 'miRNA and fracture healing' and 'miRNA and non-union fracture'. Any original article investigating miRNAs in fracture healing or non-union fractures was screened. Eventually, 82 studies were included in the qualitative analysis for 'miRNA and fracture healing', while 19 were selected for the 'miRNA and fracture non-union' category.

RESULTS AND CONCLUSIONS

Out of 151 miRNAs, miR-21, miR-140 and miR-214 were the most investigated miRNAs in fracture healing in general. miR-31-5p, miR-221 and miR-451-5p were identified to be regulated specifically in non-union fractures. Large heterogeneity was detected between studies investigating the role of miRNAs in fracture healing or non-union in terms of patient population, sample types and models used. Nonetheless, our approach identified some miRNAs with the potential to serve as biomarkers for non-union fractures, including miR-31-5p, miR-221 and miR-451-5p. We provide a discussion of involved pathways and suggest on alignment of future research in the field.

Mesenchymal Stem Cell-derived Exosomes Affect Macrophage Phenotype: A Cell-free Strategy for the Treatment of Skeletal Muscle Disorders

The process of tissue damage, repair, and regeneration in the skeletal muscle system involves complex inflammatory processes. Factors released in the inflammatory microenvironment can affect the phenotypic changes of macrophages, thereby changing the inflammatory process, making macrophages an important target for tissue repair treatment. Mesenchymal stem cells exert anti-inflammatory effects by regulating immune cells. In particular, exosomes secreted by mesenchymal stem cells have become a new cell-free treatment strategy due to their low tumorigenicity and immunogenicity. This article focuses on the mechanism of the effect of exosomes derived from mesenchymal stem cells on the phenotype of macrophages after skeletal muscle system injury and explores the possible mechanism of macrophages as potential therapeutic targets after tissue injury.

Long Non-Coding RNAs Within Macrophage-Derived Exosomes Promote BMSC Osteogenesis in a Bone Fracture Rat Model

Purpose

To investigate the effect of macrophage exosomal long non-coding (lnc)RNAs on bone mesenchymal stem cell (BMSC) osteogenesis and the associated mechanism.

Methods

Rat BMSCs and spleen macrophages were co-cultured with serum derived from the fracture microenvironment of rat tibia. BMSC osteogenesis was evaluated using Alizarin red staining and the expression of BMP-2, RUNX2, OPN, and OC mRNA. BMSC osteogenesis was evaluated after co-culture with macrophages stimulated using hypoxic conditions or colony-stimulating factor (CSF). The uptake of macrophage-derived exosomes by BMSCs was evaluated using the exosome uptake assay. High-throughput sequencing and bioinformatics analyses were performed to identify key lncRNAs in the macrophage exosomes. The effect of lncRNA expression levels on BMSC osteogenesis was also assessed using a lncRNA overexpression plasmid and siRNA technology. M1 and M2 macrophages were distinguished using flow cytometry and the key exosomal lncRNA was detected by in situ hybridization.

Results

In the fracture microenvironment, macrophages (stimulated using either hypoxia or CSF) significantly increased the osteogenic ability of BMSCs. We showed that BMSCs assimilated macrophage-derived vesicles and that the inhibition of exosomal secretion significantly attenuated the macrophage-mediated induction of BMSC osteogenesis. The hypoxia condition led to the up-regulation of 310 lncRNAs and the down-regulation of 575 lncRNAs in macrophage exosomes, while CSF stimulation caused the up-regulation of 557 lncRNAs and the down-regulation of 407 lncRNAs. In total, 108 lncRNAs were co-up-regulated and 326 lncRNAs were co-down-regulated under both conditions. We eventually identified LOC103691165 as a key lncRNA that promoted BMSC osteogenesis and was expressed at similar levels in both M1 and M2 macrophages.

Conclusion

In the fracture microenvironment, M1 and M2 macrophages promoted BMSC osteogenesis by secreting exosomes containing LOC103691165.

Osteoimmune Interactions and Therapeutic Potential of Macrophage-Derived Small Extracellular Vesicles in Bone-Related Diseases

Due to the aging of the global population, the burden of bone-related diseases has increased sharply. Macrophage, as indispensable components of both innate immune responses and adaptive immunity, plays a considerable role in maintaining bone homeostasis and promoting bone establishment. Small extracellular vesicles (sEVs) have attracted increasing attention because they participate in cell cross-talk in pathological environments and can serve as drug delivery systems. In recent years, an increasing number of studies have expanded our knowledge about the effects of macrophage-derived sEVs (M-sEVs) in bone diseases via different forms of polarization and their biological functions. In this review, we comprehensively describe on the application and mechanisms of M-sEVs in various bone diseases and drug delivery, which may provide new perspectives for treating and diagnosing human bone disorders, especially osteoporosis, arthritis, osteolysis, and bone defects.

Exosomes: A new option for osteoporosis treatment

Osteoporosis is a systemic bone disease characterized by reduced bone mass and destruction of bone microarchitecture, leading to increased bone fragility and susceptibility to fracture. However, the pathogenesis and molecular mechanisms of this disease remain unclear. Extracellular vesicles, structures originating from the plasma membrane and ranging from 30 nm to 5 µm in diameter, play an important role in intercellular communication in the bone microenvironment. Exosomes are extracellular vesicles that deliver cargo molecules, including endogenous proteins, lipids and nucleic acids. These cargo molecules are encapsulated in a lipid bilayer and internalized by target cells through receptor-ligand interactions or lipid membrane fusion. With the advancement of exosome research, exosome therapy for osteoporosis is fast becoming a research hotspot for researchers. This review aims to discuss the role of exosomes in the pathogenesis of osteoporosis. In addition, emerging diagnostic and therapeutic properties of exosomes are described to highlight the potential role of exosomes in osteoporosis.

Comprehensive analysis of M2 macrophage-derived exosomes facilitating osteogenic differentiation of human periodontal ligament stem cells

BACKGROUND

The role of periodontal ligament stem cells (PDLSCs) and macrophage polarization in periodontal tissue regeneration and bone remodeling during orthodontic tooth movement (OTM) has been well documented. Nevertheless, the interactions between macrophages and PDLSCs in OTM remain to be investigated. Consequently, the present study was proposed to explore the effect of different polarization states of macrophages on the osteogenic differentiation of PDLSCs.

METHODS

After M0, M1 and M2 macrophage-derived exosomes (M0-exo, M1-exo and M2-exo) treatment of primary cultured human PDLSCs, respectively, mineralized nodules were observed by Alizarin red S staining, and the expression of ALP and OCN mRNA and protein were detected by RT-qPCR and Western blotting, correspondingly. Identification of differentially expressed microRNAs (DE-miRNA) in M0-exo and M2-exo by miRNA microarray, and GO and KEGG enrichment analysis of DE-miRNA targets, and construction of protein-protein interaction networks.

RESULTS

M2-exo augmented mineralized nodule formation and upregulated ALP and OCN expression in PDLSCs, while M0-exo had no significant effect. Compared to M0-exo, a total of 52 DE-miRNAs were identified in M2-exo. The expression of hsa-miR-6507-3p, hsa-miR-4731-3p, hsa-miR-4728-3p, hsa-miR-3614-5p and hsa-miR-6785-3p was significantly down-regulated, and the expression of hsa-miR-6085, hsa-miR-4800-5p, hsa-miR-4778-5p, hsa-miR-6780b-5p and hsa-miR-1227-5p was significantly up-regulated in M2-exo compared to M0-exo. GO and KEGG enrichment analysis revealed that the downstream targets of DE-miRNAs were mainly involved in the differentiation and migration of multiple cells.

CONCLUSIONS

In summary, we have indicated for the first time that M2-exo can promote osteogenic differentiation of human PDLSCs, and have revealed the functions and pathways involved in the DE-miRNAs of M0-exo and M2-exo and their downstream targets.

The crosstalk between macrophages and bone marrow mesenchymal stem cells in bone healing

Bone injury plagues millions of patients worldwide every year, and it demands a heavy portion of expense from the public medical insurance system. At present, orthopedists think that autologous bone transplantation is the gold standard for treating large-scale bone defects. However, this method has significant limitations, which means that parts of patients cannot obtain a satisfactory prognosis. Therefore, a basic study on new therapeutic methods is urgently needed. The in-depth research on crosstalk between macrophages (Mϕs) and bone marrow mesenchymal stem cells (BMSCs) suggests that there is a close relationship between inflammation and regeneration. The in-depth understanding of the crosstalk between Mϕs and BMSCs is helpful to amplify the efficacy of stem cell-based treatment for bone injury. Only in the suitable inflammatory microenvironment can the damaged tissues containing stem cells obtain satisfactory healing outcomes. The excessive tissue inflammation and lack of stem cells make the transplantation of biomaterials necessary. We can expect that the crosstalk between Mϕs and BMSCs and biomaterials will become the mainstream to explore new methods for bone injury in the future. This review mainly summarizes the research on the crosstalk between Mϕs and BMSCs and also briefly describes the effects of biomaterials and aging on cell transplantation therapy.

MicroRNA-loaded biomaterials for osteogenesis

The large incidence of bone defects in clinical practice increases not only the demand for advanced bone transplantation techniques but also the development of bone substitute materials. A variety of emerging bone tissue engineering materials with osteogenic induction ability are promising strategies for the design of bone substitutes. MicroRNAs (miRNAs) are a class of non-coding RNAs that regulate intracellular protein expression by targeting the non-coding region of mRNA3′-UTR to play an important role in osteogenic differentiation. Several miRNA preparations have been used to promote the osteogenic differentiation of stem cells. Therefore, multiple functional bone tissue engineering materials using miRNA as an osteogenic factor have been developed and confirmed to have critical efficacy in promoting bone repair. In this review, osteogenic intracellular signaling pathways mediated by miRNAs are introduced in detail to provide a clear understanding for future clinical treatment. We summarized the biomaterials loaded with exogenous cells engineered by miRNAs and biomaterials directly carrying miRNAs acting on endogenous stem cells and discussed their advantages and disadvantages, providing a feasible method for promoting bone regeneration. Finally, we summarized the current research deficiencies and future research directions of the miRNA-functionalized scaffold. This review provides a summary of a variety of advanced miRNA delivery system design strategies that enhance bone regeneration.

Macrophages with Different Polarization Phenotypes Influence Cementoblast Mineralization through Exosomes

Root resorption is a common dental challenge that can lead to tooth loosening or even tooth loss. Among the cells involved in root resorption, cementoblasts are responsible for laying down the cementum, while macrophages with different phenotypes have also been shown to have bidirectional effects on root resorption. However, the relationship between macrophages and cementoblasts remains largely unknown. In this study, we examined the effect of macrophages with different polarization phenotypes on the mineralization of cementoblasts. Using the transwell coculture system and a conditioned medium-based coculture system, we found that compared with M0 (unpolarized macrophages), M1-polarized macrophages attenuated cementoblast mineralization, while M2-polarized macrophages enhanced cementoblast mineralization. Furthermore, by extracting M0/M1/M2 macrophage exosomes and examining their effects on the mineralization of cementoblasts, we found that the effects of macrophages on cementoblast mineralization were, at least partially, exerted by exosomes. Moreover, in vivo studies also indicated that an increased M1/M2 ratio could suppress cementoblast mineralization and bring about root resorption. During mechanical force-induced orthodontic tooth movement (OTM), root resorption was evident on the compression side of periodontal tissue, and a higher M1/M2 ratio and weaker cementoblast mineralization were observed on the compression side than on the tension side. We also used localized lipopolysaccharide (LPS) injection to increase the M1/M2 ratio around the roots of maxillary molars, where root resorption and decreased cementoblast mineralization were also observed. Furthermore, when we injected the exosomes from M0 and M1- and M2-polarized macrophages into mice, it was observed that the cementoblast mineralization was attenuated in the group injected with M1-polarized macrophage exosomes, while it was augmented in the group injected with M2-polarized macrophage exosomes.

The promising roles of macrophages in geriatric hip fracture

As aging becomes a global burden, the incidence of hip fracture (HF), which is the most common fracture in the elderly population and can be fatal, is rapidly increasing, and its extremely high fatality rate places significant medical and financial burdens on patients. Fractures trigger a complex set of immune responses, and recent studies have shown that with aging, the immune system shows decreased activity or malfunctions in a process known as immune senescence, leading to disease and death. These phenomena are the reasons why elderly individuals typically exhibit chronically low levels of inflammation and increased rates of infection and chronic disease. Macrophages, which are key players in the inflammatory response, are critical in initiating the inflammatory response, clearing pathogens, controlling the innate and adaptive immune responses and repairing damaged tissues. Tissue-resident macrophages (TRMs) are widely present in tissues and perform immune sentinel and homeostatic functions. TRMs are combinations of macrophages with different functions and phenotypes that can be directly influenced by neighboring cells and the microenvironment. They form a critical component of the first line of defense in all tissues of the body. Immune system disorders caused by aging could affect the biology of macrophages and thus the cascaded immune response after fracture in various ways. In this review, we outline recent studies and discuss the potential link between monocytes and macrophages and their potential roles in HF in elderly individuals.

The Roles of Exosomes upon Metallic Ions Stimulation in Bone Regeneration

Metallic ions have been widely investigated and incorporated into bone substitutes for bone regeneration owing to their superior capacity to induce angiogenesis and osteogenesis. Exosomes are key paracrine mediators that play a crucial role in cell-to-cell communication. However, the role of exosomes in metallic ion-induced bone formation and their underlying mechanisms remain unclear. Thus, this review systematically analyzes the effects of metallic ions and metallic ion-incorporated biomaterials on exosome secretion from mesenchymal stem cells (MSCs) and macrophages, as well as the effects of secreted exosomes on inflammation, angiogenesis, and osteogenesis. In addition, possible signaling pathways involved in metallic ion-mediated exosomes, followed by bone regeneration, are discussed. Despite limited investigation, metallic ions have been confirmed to regulate exosome production and function, affecting immune response, angiogenesis, and osteogenesis. Although the underlying mechanism is not yet clear, these insights enrich our understanding of the mechanisms of the metallic ion-induced microenvironment for bone regeneration, benefiting the design of metallic ion-incorporated implants.

Macrophage miR-149-5p induction is a key driver and therapeutic target for BRONJ

Bisphosphonate-related (BP-related) osteonecrosis of the jaw (BRONJ) is one of the severe side effects of administration of BPs, such as zoledronic acid (ZA), which can disrupt the patient’s quality of life. Although the direct target of skeletal vasculature and bone resorption activity by BPs has been phenomenally observed, the underlying mechanism in BRONJ remains largely elusive. Thus, it is urgently necessary to discover effective therapeutic targets based on the multifaceted underlying mechanisms in the development of BRONJ. Here, we determined the inhibitory role of ZA-treated macrophages on osteoclast differentiation and type H vessel formation during tooth extraction socket (TES) healing. Mechanistically, ZA activated the NF-κB signaling pathway and then induced p65 nuclear translocation in macrophages to promote miR-149-5p transcription, resulting in impaired osteoclast differentiation via directly binding to the Traf6 3′-UTR region. Moreover, we identified that miR-149-5p–loaded extracellular vesicles derived from ZA-treated bone marrow–derived macrophages could regulate biological functions of endothelial cells via the Rap1a/Rap1b/VEGFR2 pathway. Furthermore, local administration of chemically modified antagomiR-149-5p was proven to be therapeutically effective in BRONJ mice. In conclusion, our findings illuminate the dual effects of miR-149-5p on skeletal angiogenesis and bone remolding, suggesting it as a promising preventive and therapeutic target for BRONJ.